1. Field of the Invention
The present invention relates to a silicon ingot for a solar cell, and more particularly, to an apparatus and method of extracting a silicon ingot capable of extracting the silicon ingot through two steps to reduce the height of an apparatus for extracting the silicon ingot.
2. Discussion of Related Art
A silicon wafer, which has been traditionally used as a substrate for a solar cell, is manufactured by thinly cutting a directionally solidified silicon ingot. Here, quality and cost of the silicon wafer are determined by quality and cost of the silicon ingot.
Accordingly, in order to increase the quality of the silicon wafer and reduce the cost thereof, manufacturing cost of a high quality directionally solidified silicon ingot should be reduced. For this, an electromagnetic continuous casting method using a crucible formed of graphite or quartz, which is a casting material for solidifying the ingot, with no casting loss, has begun being used.
A conventional electromagnetic continuous casting method uses a cold crucible for continuous casting, which is manufactured by an induction coil and a conductive material (in general, using oxygen-free copper) disposed inside the induction coil, and a lower portion of which is open. At least a circumferential portion of the cold crucible has a structure divided into a plurality of segments by longitudinal slits, i.e., a water cooling structure through which cooling water passes to solidify a molten metal and protect a cold crucible.
The longitudinal slits allow a magnetic field generated by a radio frequency current flowing through the induction coil to flow into the cold crucible to generate an induction current from a dissolved source material, and thus, Joule's heating effect caused thereby heats and dissolves a continuously supplied charged source material, and generates an electromagnetic force toward the inside of the cold crucible, reducing contact between the dissolved source material and the cold crucible.
In addition, a dissolved silicon solution flows downward along the cold crucible while being solidified, and when a source material is continuously supplied, a directionally solidified ingot can be continuously manufactured.
Since such an electromagnetic continuous casting method reduces contact with the cold crucible, contamination of the source material is suppressed and quality of the ingot is improved, and simultaneously, the casting is not consumed, so that maintenance cost is reduced and productivity is improved.
However, the above-mentioned conventional electromagnetic continuous casting method has the following problems.
First, the conventional electromagnetic continuous casting apparatus should increase yield of each batch to accomplish mass production. However, since continuous casting must be performed in a vertical direction, the size of equipment should be increased exponentially according to an increase in yield. When the size of the equipment is increased as described above, floor height of a building, etc. must be sufficiently secured and thus equipment investment must be increased.
Next, in the conventional art, a sufficient stroke of an extraction apparatus must be secured to stably extract the ingot to a designed length at an appropriate extraction speed and take the extracted ingot out of the apparatus. For example, in order to extract the silicon ingot having a length of 1 m, a stroke of 2 m, which is at least two times of the ingot length, must be secured.
For the purpose of easier description, FIGS. 1 to 3 are operation views showing a process of extracting a silicon ingot using the conventional art.
Referring to FIG. 1, a chamber 1 includes a gas inlet 2 and a gas outlet 3. A silicon source material introduced into a cold crucible is melted in the chamber 1. The molten silicon is solidified in the chamber 1 to be manufactured as an ingot 5.
The ingot 5 is supported by a dummy block 7 at its lower end, and a lower end of the dummy block 7 is coupled to a shaft 9. The shaft 9, which is vertically movably installed, is lowered to extract the ingot 5. The shaft 9 is supported by a shaft holder 10, and the shaft 9 is fastened to a screw 11 and a shaft guide 13 to move therewith.
Meanwhile, the shaft holder 10 vertically moves along the shaft guide 13 lengthily installed in the vertical direction, and the screw 11 is supported by a support plate 14 at its lower end.
In the conventional art, the height of the shaft guide 13 is about 2 L as shown. This is because a stroke of L is further needed such that the shaft 9 extracts the ingot 5 having a height of L and discharges the ingot to the outside. Referring to FIG. 2, since the ingot 5 is disposed in the chamber 1 even when the shaft 9 lowers the ingot 5 to a height of L, the ingot 5 can be discharged to the outside only when the ingot is further lowered by the stroke of L as shown in FIG. 3.
As described above, the secured stroke of the extraction apparatus eventually increases the size of equipment and cost in equipment investment.